In recent years, a technique of scrolling is known as a way for displaying a large volume of information that can not fit into a screen. The scrolling technique moves a content of the screen in an upward/downward/leftward/rightward direction for displaying a portion of information that spilled over from the screen. However, scrolling through a large volume of information requires time and effort due to the amount of the information to be scrolled. In addition, the content of information cannot be grasped during scrolling when scrolling speed is increased.
A scale of the image displayed on the screen is changed by zooming in and zooming out. That is, the image “zooms in” when the scale (i.e., a shrinking factor) of the image is decreased, and the image “zooms out” when the scale of the image is increased. The spilled-over content can be included in the screen when the image is zoomed out.
A large portion of conventional screen display apparatuses are configured to have different interfaces respectively for scrolling and zooming control. Therefore, the scrolling operation and the zooming operation had to be frequently changed for finding a desired portion of a large volume image. The frequent change of the scrolling operation and the zooming operation caused hassles to a user of the screen display apparatus. For example, the image in the screen had to be zoomed out for roughly locating desired information in the zoomed-out image at first, and then the image had to be zoomed in for closely searching the desired information.
A non-patent document 1 discloses a technique that resolves the hassles of the above operation by combining the scrolling and the zooming. This document discloses an interface that automatically controls a zoom level based on a speed of the scroll operation. This document proposes a basic concept of a constant scroll speed on the screen regardless of an actual speed in the information space. In this manner, the scrolling speed that is too fast to be caught by the eye is prevented. Further, this non-patent document proposes a plan that prevents an abrupt zooming out in a high-speed scroll by calculating the zoom level based on a power of an input value.
[Non-patent document 1] “Effective navigation by an automatic zooming according to a movement speed” by Takeo Igarashi, Ken Hinckley in a proceeding for 8th workshop of interactive systems and software (WISS2000), pp. 57-66, December 2000.
However, the technique in the above-identified non-patent document 1 is that the speed of the scrolling on the screen (i.e., a visual speed of screen) is kept at a constant rate, thereby being unable to scroll through the information space over the scroll speed inputted from an input device. For example, even when the input value of the scroll speed doubles, the scrolling speed is visually kept constant on the screen where the zoom level is changed to ½. In other words, the information space is not scrolled through as twice as fast by this technique. Therefore, it takes a long time to find the desired information in the large volume of information such as a map or the like.
Further, when a relationship between the input value from the input device and the scroll speed are set so as to access the information far apart in the information space in an appropriate period, the zoom level becomes susceptible to a small change in the input value to cause a large scale change due to the gap of a range of the input value and the scale of the information space as well as the restriction on the input range of the input device. Particularly, when the information such as a map or the like is equally beneficial at any level between the zoomed-in image and the zoomed-out image, a frequent change of the zoom rate causes problems for practical use.